I'm connected to a vCenter server and this is what I see when checking the metrics I have available:
$aaa = Get-Stat -Entity SomeVM
#when running this I get an error saying metric counter 'disk.usage.average' doesn't exist
$aaa | group -property metricid
#I only see these metrics:
cpu.usage.average
cpu.usagemhz.average
mem.usage.average
net.usage.average
sys.uptime.latest